Glass optical fiber is typically produced by drawing from a solid glass rod, to be termed herein the "preform". In some widely practiced preform manufacturing processes (e.g., the Modified Chemical Vapor Deposition (MCVD) process), the preform is produced by collapsing a tubular body consisting of a silica substrate tube and, deposited thereon, high-purity glass formed from precursor material in a glass-forming reaction. Furthermore, in a version of the Vapor Axial Deposition (VAD) process, a silica tube, the "sleeve" tube, is collapsed around a core consisting of deposited glass material. Thus, collapsing a silica tube to a smaller diameter, including to solid rod form, is a common optical fiber manufacturing step.
Although materials other than silica are potentially usfeul for optical fibers, at least for communication purposes the fibers of choice currently are high-silica fibers. However, the refractory nature of silica leads to some production difficulties. For instance, the above referred-to collapse typically has to be carried out at very high temperatures (typically in excess of 2,000.degree. C., typically obtained by means of one (or more) reciprocating oxy-hydrogen torches), and typically requires considerable time, of the order of hours. Since preform fabrication costs constitute a significant part of the cost of optical fiber production, and since, furthermore, the time required for producing a preform is a very significant component of preform fabrication cost, process changes that result in decreased collapse time would be of obvious economic significance. This application discloses such a change that results in substantial decrease of collapse time without, at the same time, having a deleterious effect on fiber properties, and which can be implemented easily and at very low cost.
Since the instant invention comprises deuteration of silica tubes, brief reference will now be made to prior art uses of deuterium in optical fiber manufacture.
U.S. Pat. No. 3,791,714, issued Feb. 12, 1974 to R. D. Maurer, for "Method of Producing Glass for Optical Waveguides," discloses that glass having low hydroxyl ion content can be produced by means of flame hydrolysis, the process comprising passing deuterium gas, or a deuterium compound gas, through a liquid containing a silicon compound such as silicon tetrachloride, and burning the resulting vapor to deposite a film comprising silicon deuteride on a rotating mandrel.
J. Stone and C. A. Burrus, Bell System Technical Journal, Vol. 59(8), pages 1541-1548 (1980), disclose that deuterium/hydrogen exchange in silica-based glass can be used to produce low loss optical fibers by decreasing OH-loss. A similar approach was disclosed by E. Modone and G. Roba, Electronics Letters, Vol. 17(21), pages 815-817 (1981). See also European patent application No. EP81 10 4458, filed June 11, 1981, by E. Modone et al, for "Process for Reducing the Hydroxyl-Group Content in Preforms for Optical Fibers Manufactured by MCVD Process".